Biswakarma Jagannath, Matthews Molly, Byrne James M
School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, United Kingdom.
Environ Sci Technol Lett. 2024 Oct 15;11(11):1239-1246. doi: 10.1021/acs.estlett.4c00700. eCollection 2024 Nov 12.
Arsenic is a global pollutant. Recent studies found that Fe(II) can oxidize As(III), but the extent of oxidation with mixed-valent iron minerals and the mechanisms involved are unknown. In this study, we investigated whether As(III) can be oxidized under reducing conditions using green rust sulfate (GR-SO), an Fe mineral containing both Fe(II) and Fe(III). Batch sorption experiments showed that GR-SO (1 g L) effectively sorbs environmentally relevant concentrations of As(III) (50-500 μg L) under anoxic, neutral pH conditions with and without citrate (50 μM). X-ray absorption near-edge structure spectroscopy analysis at the As K-edge demonstrated that approximately 76% of As(III) was oxidized to As(V) by GR-SO. Complete oxidation of As(III) was observed in the presence of citrate. As(III) oxidation can be linked to the phase transformation of GR-SO to goethite, resulting in new reactive Fe(III) species that plausibly drive oxidation. Citrate enhanced this process by stabilizing Fe on the mixed GR-SO/goethite surface, preventing its reduction back to Fe(II) and facilitating further As(III) oxidation without significant Fe loss to the solution. This study highlights the cryptic As(III) oxidation that occurs under reducing conditions, providing new insights into the cycling of arsenic in mixed phases of iron-rich, anoxic environments.
砷是一种全球污染物。最近的研究发现，Fe(II) 可以氧化 As(III)，但混合价态铁矿物的氧化程度以及相关机制尚不清楚。在本研究中，我们研究了在还原条件下，使用含有 Fe(II) 和 Fe(III) 的铁矿物——绿锈硫酸盐（GR-SO），As(III) 是否能够被氧化。批量吸附实验表明，在缺氧、中性pH条件下，无论有无柠檬酸盐（50 μM），GR-SO（1 g/L）都能有效吸附环境相关浓度的 As(III)（50 - 500 μg/L）。As K 边的 X 射线吸收近边结构光谱分析表明，大约76% 的 As(III) 被 GR-SO 氧化为 As(V)。在柠檬酸盐存在的情况下，观察到 As(III) 完全氧化。As(III) 的氧化可能与 GR-SO 向针铁矿的相变有关，从而产生可能驱动氧化的新的活性 Fe(III) 物种。柠檬酸盐通过稳定 GR-SO/针铁矿混合表面上的 Fe，防止其还原回 Fe(II)，并促进进一步的 As(III) 氧化，而不会有大量 Fe 损失到溶液中，从而增强了这一过程。本研究强调了在还原条件下发生的隐秘的 As(III) 氧化，为富铁缺氧环境混合相中砷的循环提供了新的见解。
